Power distribution plate for powering internal control rod drive mechanism (CRDM) units

ABSTRACT

A power distribution plate (PDP) sits on top of a support plate. Control rod drive mechanism (CRDM) units are mounted on top of the PDP, but the PDP is incapable of supporting the weight of the CRDM units and instead transfers the load to a support plate. The PDP has receptacles which receive cable modules each including mineral insulated (MI) cables, the MI cables being connected with the CRDM units. The PDP may further include a set of hydraulic lines underlying the cable modules and connected with the CRDM units. The cable modules in their receptacles define conduits or raceways for their MI cables and for any underlying hydraulic lines.

BACKGROUND

The following relates to the nuclear reactor arts, nuclear powergeneration arts, nuclear reactor control arts, nuclear reactorelectrical power distribution arts, and related arts.

In nuclear reactor designs of the integral pressurized water reactor(integral PWR) type, a nuclear reactor core is immersed in primarycoolant water at or near the bottom of a pressure vessel. In a typicaldesign, the primary coolant is maintained in a subcooled liquid phase ina cylindrical pressure vessel that is mounted generally upright (thatis, with its cylinder axis oriented vertically). A hollow cylindricalcentral riser is disposed concentrically inside the pressure vessel.Primary coolant flows upward through the reactor core where it isheated, rises through the central riser, discharges from the top of thecentral riser, and reverses direction to flow downward back toward thereactor core through a downcomer annulus.

The nuclear reactor core is built up from multiple fuel assemblies. Eachfuel assembly includes a number of fuel rods. Control rods comprisingneutron absorbing material are inserted into and lifted out of thereactor core to control core reactivity. The control rods are supportedand guided through control rod guide tubes inside the reactor core andby guide tube frames outside the core. In the integral PWR design, atleast one steam generator is located inside the pressure vessel (i.e.“integral with” the reactor), typically in the downcomer annulus, andthe pressurizer is located at the top of the pressure vessel, with asteam space as the top most point of the reactor. Alternatively anexternal pressurizer can be used to control reactor pressure.

A set of control rods is arranged as a control rod assembly thatincludes the control rods connected at their upper ends with a yoke orspider, and a connecting rod extending upward from the spider. Thecontrol rod assembly is raised or lowered to move the control rods outof or into the reactor core using a control rod drive mechanism (CRDM).In a typical CRDM configuration, an electrically driven motor ormagnetic assembly selectively rotates a roller nut assembly or otherthreaded element that engages a lead screw that in turn connects withthe connecting rod of the control rod assembly. The control rods aretypically also configured to “SCRAM”, by which it is meant that thecontrol rods can be quickly released in an emergency so as to fall intothe reactor core under force of gravity and quickly terminate thepower-generating nuclear chain reaction. Toward this end, the roller nutassembly may be configured to be separable so as to release the controlrod assembly and lead screw which then fall toward the core as atranslating unit. In another configuration, the connection of the leadscrew with the connecting rod is latched and SCRAM is performed byreleasing the latch so that the control rod assembly falls toward thecore while the lead screw remains engaged with the roller nut. SeeStambaugh et al., “Control Rod Drive Mechanism for Nuclear Reactor”,U.S. Pub. No. 2010/0316177 A1 published Dec. 16, 2010 which isincorporated herein by reference in its entirety; and DeSantis, “ControlRod Drive Mechanism for Nuclear Reactor”, U.S. Pub. No. 2011/0222640 A1published Sep. 15, 2011 which is incorporated herein by reference in itsentirety.

The CRDMs are complex precision devices which typically include anelectric motor requiring electrical power, and may also requirehydraulic, pneumatic, or another source of power to overcome the passiveSCRAM release mechanism (e.g., to hold the separable roller nut in theengaged position, or to maintain latching of the connecting rod latch)unless this is also electrically operated (e.g., an electromagneticclamp that releases upon removal of electrical power). In existingcommercial nuclear power reactors, the CRDMs are located externally,i.e. outside of the pressure vessel, typically above the vessel in PWRdesigns, or below the reactor in boiling water reactor (BWR) designs. Anexternal CRDM has the advantage of accessibility for maintenance and canbe powered through external electrical and hydraulic connectors.However, the requisite mechanical penetrations into the pressure vesselpresent safety concerns. Additionally, in compact integral PWR designs,especially those employing an integral pressurizer, it may be difficultto configure the reactor design to allow for overhead external placementof the CRDMs. Accordingly, internal CRDM designs have been developed.See U.S. Pub. No. 2010/0316177 A1 and U.S. Pub. No. 2011/0222640 A1which are both incorporated herein by reference in their entireties.

However, a difficulty with this approach is that it entails extensiveelectrical (and possibly hydraulic and/or pneumatic) cabling inside thereactor pressure vessel. For example, if there are sixty nine CRDM unitswith three electrical cables per CRDM unit (e.g., power, positionindicator, and ground), then 207 electrical cables are required for thesixty nine units. The locations of the CRDM units are substantiallyconstrained, e.g. all CRDM units are above the reactor core in the caseof a PWR, and at a distance from the core effective to allow the CRDMunits to move the control rod assemblies into or out of the core. Anapproach for relaxing the positioning constraint is to staggerneighboring CRDM units vertically, as disclosed in U.S. Pub. No.2011/0222640 A1. However, the space for the electrical cabling is stilltight. Electrical cabling in a nuclear reactor is typically in the formof mineral insulated (MI) cables, which have limited bend radiusspecifications. Cabling operations such as splicing or joining cables iscomplex for MI cables, because the mineral insulation can be damaged bywater exposure. The SCRAM function is safety-related, and so nuclearsafety regulations may require shutdown of the reactor if even one CRDMunit becomes non-operative, making reliability of this extensive MIcabling of especial importance.

Disclosed herein are improvements that provide various benefits thatwill become apparent to the skilled artisan upon reading the following.

BRIEF SUMMARY

In one illustrative embodiment, a nuclear reactor comprises a pressurevessel containing primary coolant water and further containing: anuclear reactor core comprising fissile material; a mounting plate; aset of electric devices mounted on the mounting plate wherein the set ofelectric devices is one of (1) a set of control rod drive mechanism(CRDM) units and (2) a set of reactor coolant pumps (RCPs); adistribution plate; and a plurality of cable modules mounted inreceptacles of the distribution plate. Each cable module includesmineral insulated (MI) cables connected with one or more of the electricdevices, the cable module including its MI cables being removable as aunit from the receptacle of the distribution plate.

In another illustrative embodiment, a nuclear reactor comprises apressure vessel containing primary coolant water and further containing:a nuclear reactor core comprising fissile material; a mounting plate; adistribution plate mounted on the mounting plate; and a set of electricdevices mounted on the distribution plate. The distribution plateincludes mineral insulated (MI) cables disposed in or on thedistribution plate and connected with the set of electric devices. Theset of electric devices is one of (1) a set of control rod drivemechanism (CRDM) units and (2) a set of reactor coolant pumps (RCPs).The distribution plate is incapable of supporting the weight of the setof electric devices, the distribution plate transferring weight of theset of electric devices to the mounting plate which supports thecombined weight of both the set of electric devices and the distributionplate. The distribution plate in some embodiments comprises a platehaving a plurality of grooves, and cable modules disposed in the groovesof the plate, each cable module including a portion of the MI cablesdisposed on or in the distribution plate, each cable module includingits portion of the MI cables being removable from the plate as a unit.

In another illustrative embodiment, an electrical distribution platecomprises a plate having a plurality of receptacles, and cable modulesdisposed in the receptacles of the plate. Each cable module includesmineral insulated (MI) cables, and each cable module including its MIcables is removable from the plate as a unit. Each cable module whenmounted in its receptacle of the plate defines a conduit or racewaythrough which its MI cables run. In some embodiments, each cable moduleincludes electrical connectors that are externally accessible when thecable module is mounted in its receptacle of the plate.

In another illustrative embodiment, a nuclear reactor comprises: apressure vessel; a nuclear reactor core comprising fissile materialdisposed in the pressure vessel; an electrical distribution plate as setforth in the immediately preceding paragraph disposed in the pressurevessel; and a set of electrical devices electrically connected with theMI cables of the cable modules of the electrical distribution plate. Insome embodiments the set of electrical devices is a set of control roddrive mechanism (CRDM) units.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various components and arrangements ofcomponents, and in various process operations and arrangements ofprocess operations. The drawings are only for purposes of illustratingpreferred embodiments and are not to be construed as limiting theinvention.

FIG. 1 diagrammatically shows an integral pressurized water reactor(integral PWR) with the upper internals of the reactor inset.

FIG. 2 shows a perspective view of a distribution plate suitably used inthe upper internals of the integral PWR of FIG. 1.

FIG. 3 diagrammatically shows an alternative embodiment of adistribution plate having openings for modules.

FIG. 4 diagrammatically shows a support plate for use with thedistribution plate of FIG. 3.

FIG. 5 illustrates an overhead view of the distribution plate of FIG. 3with modules installed.

FIG. 6 illustrates an enlarged view of a portion of the plate withmodules installed of FIG. 5, with the footprints of four installed CRDMstandoffs indicated by dotted lines.

FIGS. 7 and 8 illustrate two alternative perspective views of anelectrical and hydraulic module for use with the distribution plate ofFIG. 3.

FIGS. 9 and 10 illustrate two alternative perspective views of a rodposition indication and rod bottom module for use with the distributionplate of FIG. 3.

FIG. 11 diagrammatically shows the route of electrical or hydrauliclines within the distribution plate of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an integral pressurized water reactor (integral PWR)generally designated by the numeral 10. A reactor vessel 11 is generallycylindrical and contains primary coolant water, a reactor core 1, one ormore steam generators 2, and a pressurizer 3. A central riser 4separates a hot leg of the primary coolant circuit flowing upwardthrough the central riser 4 from a cold leg of the primary coolantcircuit flowing downward through a downcomer annulus defined between thecentral riser 4 and the pressure vessel 11. The one or more steamgenerators are suitably disposed in the downcomer annulus. Although apressurized water reactor (PWR) is depicted, a boiling water reactor(BWR) or other type of nuclear reactor is also contemplated. The reactor10 is an illustrative example, and numerous variants are contemplated,such as replacing the pressurizer 3 with an external pressurizer,employing external steam generators, and so forth. Moreover, while thedisclosed rapid installation and servicing techniques are described withreference to illustrative internal CRDM units, these techniques arereadily adapted for use with other internal nuclear reactor componentssuch as internal reactor coolant pumps.

In the illustrative PWR, above the core 1 are the reactor upperinternals 12 of integral PWR 10, shown in inset. In the illustrative PWR10, the upper internals 12 are supported laterally by a mid-flange 14,which in the illustrative embodiment also supports internal cannedreactor coolant pumps (RCPs) 16. More generally, the RCPs may beexternal pumps or have other configurations (or, RCPs may be omittedentirely and the reactor may rely upon natural circulation of primarycoolant), and the upper internals may be supported otherwise than by theillustrative mid flange 14. The upper internals include control rodguide frames 18 to guide the control rod assemblies for controlling thenuclear chain reaction in the core 1. Control rod drive mechanisms(CRDMs) 20 raise and lower the control rods to control the reactor. Inaccordance with one embodiment, a CRDM distribution plate 22 supportsthe CRDMs and provides power and/or hydraulics to the CRDMs. The CRDMdistribution plate may be combined with or include separate “mid-hangerplate.” A riser transition 24 connects the lower end of the centralriser 4 with a core shroud or the like to separate the hot and cold legsof the primary coolant circuit in the lower vessel region.

Control rods are withdrawn from the core 1 by the CRDMs 20 to provideenough positive reactivity to achieve criticality. Control rod guidetubes passing through the reactor core 1 and the guide frames 18 abovethe core provide space for the rods and interconnecting spider to beraised upward away from the reactor core. The CRDMs 20 include electricmotors which move the rods via a suitable mechanism such as a nut/screwmechanism, rack-and-pinion mechanism, or so forth. In illustrativeexamples, a nut-screw mechanism is assumed. For any motor drivenmechanism, electrical cables are needed to power the motor, and electriccables may also be needed for auxiliary electrical components such asrod position indicators and/or rod bottom sensors. In some designs, theforce to latch the connecting rod to the lead screw, or to maintainengagement of the separable roller nut, is hydraulic, necessitating ahydraulic connection to the CRDM. Alternatively, electric mechanisms canbe employed for these purposes, thus calling for additional electriccabling. To ensure passive safety, a positive force is usually requiredto prevent SCRAM, such that removal of the positive force initiates aSCRAM. The illustrative CRDM 20 is an internal CRDM, that is, is locatedinside the reactor vessel, and so the electrical connections to theCRDMs 20 are difficult to access. The distribution plate 22 provides astructural support for this electrical cabling. Servicing of a CRDMduring a plant shutdown should preferably be rapid in order to minimizethe length of the shutdown. To facilitate replacing a CRDM, the CRDMassembly (possibly including a standoff) is connected to thedistribution plate 22 to provide electrical power and hydraulics to theCRDM 20 via connectors that require no action to effectuate theconnection other than placement of the standoff assembly onto thedistribution plate 22. After placement, the CRDM assembly is secured tothe distribution plate by bolts or other fasteners. Additionally oralternatively, it is contemplated to rely upon the weight of the CRDM tohold the assembly in place, or to use welds to secure the assembly.

FIG. 2 illustrates one embodiment of a distribution plate 22 which is asingle plate that contains the electrical and hydraulic lines and alsois strong enough to provide support to the CRDMs and upper internalswithout reinforcement. The motor/roller nut assembly of the CRDM isgenerally located in the middle of the lead screw's travel path. Whenthe control rod is fully inserted into the core, the roller nut isholding the top of the lead screw, and, when the control rod is at thetop of the core, the roller nut is holding the bottom of the lead screwand most of the length of the lead screw extends upward above themotor/roller nut assembly. Hence the distribution plate 22 that supportsthe CRDM is positioned “below” the CRDM units and a relatively shortdistance above the reactor core.

FIG. 2 shows the distribution plate 22 with a single standoff assembly24 mounted for illustration, though it should be understood that allopenings 26 would have a standoff assembly (and accompanying CRDM)mounted in place during operation of the reactor. Each opening 26 allowsa lead screw of a control rod to pass through and the periphery of theopening provides a connection site for a standoff assembly that supportsthe CRDM. The lead screw passes down through the CRDM, through thestandoff assembly, and then through the opening 26. The distributionplate 22 has, either internally embedded within the plate or mounted toit, electrical power lines (e.g., electrical conductors) and hydraulicpower lines (if needed) to supply the CRDM with power and hydraulics.The illustrative openings 26 are asymmetric or keyed so that the CRDMcan only be mounted in one orientation. As illustrated, there are 69openings arranged in nine rows to form a grid, but more or fewer couldbe used depending on the number of connecting rod/CRDM units in thereactor. The distribution plate 22 is circular to fit the interior ofthe reactor, with openings 28 to allow for flow through the plate. Flowmay also be designed through the CRDMs 20, i.e. through the flowpassages 26 around or through components of the CRDMs 20. In somedesigns, not all openings 26 may have CRDMs mounted to them.

Each internal control rod drive mechanism (CRDM) unit 20 is powered byelectrical power and/or hydraulic power. In the design of FIG. 1, theCRDM units are packed closely together, which creates a high density ofelectrical and/or hydraulic cabling. The distribution plate 22facilitates efficient deployment of this extensive cabling. However, itis recognized herein that such rapid deployment preferably should beaugmented by an efficient mechanism for repair or replacement of the MIcabling and/or hydraulic cabling. Although MI cabling is robust, whichis why it is typically selected for use in a nuclear reactorenvironment, it is still susceptible to damage due to the challengingreactor environment that exposes the cabling to high temperature, highpressure and pressure cycling, radioactivity, and possibly causticchemicals (e.g., soluble boron-based chemical shim). In the event of afailure of a cable of the distribution plate 22, the failed componentwould need to be accessed and repaired in-place (which is difficult dueto the special handling required for MI cables in order to avoiddegradation due to water exposure) or the entire distribution plate 22would need to be removed (which would involve removal of all 69 CRDMunits 20 in the case of the illustrative embodiment of FIGS. 1 and 2).

With reference to FIGS. 3-11, an improved distribution plate design isdisclosed, which is constructed as a multi-component assembly. A powerdistribution plate (PDP) 40 shown in FIG. 3 provides the structuralframe for power distribution to the CRDMs 20. The illustrativeembodiment is a two-plate design in which the PDP 40 sits on top of asupport plate, for example a mid-hanger plate 50 shown in FIG. 4) andtransfers the weight of the CRDMs 20 to the support plate 50. In thistwo-plate design, the PDP 40 of FIG. 3 is not strong enough to supportthe weight of the CRDMs and instead transfers the load to the supportplate 50 shown in FIG. 4, which carries the weight of both the CRDMs 20and the PDP 40 and its installed cable modules (see FIGS. 7-10). Thetwo-plate design advantageously facilitates fabrication of the PDP 40with its relatively intricate features using machining. In oneembodiment, the PDP 40 is machined from plate stock or a forging of304L, although other materials and/or manufacturing methods arecontemplated.

In a variant two-plate design (not shown), the power distribution plateis contemplated to be mounted underneath the support plate, in whichcase the power distribution plate would not perform a load transferfunction respective to the CRDMs. As yet another contemplated variant,in a single-plate design (not shown) the PDP also provides structuralsupport for the CRDMs, in which case the PDP would be a substantiallythicker plate, formed for example by casting and/or forging.

The PDP 40 of FIG. 3 is shown without installed cable modules, so as toshow receptacles 42 into which the power cable modules 60 (FIGS. 7 and8) and sensor cable modules 70 (FIGS. 9 and 10, e.g. cables for sensorssuch as position indicators and rod bottom, i.e. PI, indicators) areinserted. The receptacles 42 are generally formed as grooves so that thecable modules 60, 70 of relatively narrow aspect-ratio can delivercabling to the interior of the PDP 40. The cable modules 60, 70 routethe electrical cables. Hydraulic lines 78 are mounted to the PDP 40 (seeFIG. 11), although it is alternatively contemplated to include thehydraulic lines in the modules as well.

FIG. 5 shows the PDP 40 with the cable modules 60, 70 installed, whileFIG. 6 shows an enlarged portion of the PDP 40 with the cable modules60, 70 installed, and with the footprints of four CRDM standoffsindicated by four dashed squares. In FIG. 5, power MI cables 61 of thepower cable modules 60 and signal MI cables 71 of the signal cablemodules 70 are diagrammatically shown. (Note that FIG. 5 is diagrammaticin that it shows the MI cables 61, 71 which are actually mostly orcompletely occluded by the tops of the installed modules 60, 70; comparewith FIGS. 7-10). The MI cables of each module run from a pigtail, inputconnector, or other electrical input located (when the module isinstalled on the PDP 40) at the periphery of the PDP 40 and run toconnectors arranged to connect with the CRDMs 20. External power inputcables run from electrical feedthroughs of the pressure vessel 11 to thepigtails or other peripheral electrical inputs of the cable module 60,70.

As seen in FIG. 6, the CRDMs 20 are mounted overlapping the cablemodules, receiving power, hydraulics, and providing signal cableconnections via the cable modules 60, 70. It will be noted that thepower cable modules 60 and the sensor cable modules 70 alternate acrossthe PDP 40, and each CRDM standoff is arranged to overlap a portion ofone power cable module 60 and a portion of one sensor cable module 70(see FIG. 6) in order to connect with both power lines and signal lines.With reference back to FIG. 3, the PDP 40 has an opening (four of whichare labeled 46 in FIG. 3) for each CRDM, which allows the lead screw,connecting rod, or other connecting element to pass through to thecontrol rods (or to the spider or yoke holding the control rods). In theillustrative embodiment shown, there are 69 such openings for the 69CRDMs 20. These openings 46 of the PDP 40 are aligned with openings 54through the support plate 50 to allow the lead screw, connecting rod, orother connecting element to pass through both the PDP 40 (via openings46) and the support plate 50 (via openings 54). Attachment points 52(see FIG. 4) connect the mid-hanger support plate 50 to the upperinternals 12. The PDP 40 of FIG. 3 also has flow slots (four of whichare labeled 44) to reduce head loss due to the PDP (that is, to reducepressure drop over the PDP 40). Aligned flow holes may be provided inthe support plate 50 as well, but are not shown.

With continuing reference to FIG. 6 and with further reference to FIGS.7 and 8, the MI cables 61 of the power cable module 60 run from theperipheral pigtail, input connector, or other electrical input at aninput station 67 to one or more connection blocks 69 of the cable module60. At each connection block 69, one or (typically) more of the MIcables terminate at electric power connections 64 that feed one of theCRDM units. The illustrative power cable module 60 has two connectionblocks 69 and six MI cables 61: three of the cables terminate at theconnection block 69 that is more proximate to the input station 67,while the remaining three MI cables continue on and terminate at theconnection block 69 that is more distal from the input station 67. Otherconfigurations are possible—for example, the uppermost and lowermostpower cable modules 60 of the distribution plate of FIG. 5 has adifferent configuration since those power cable modules are roughlyparallel with the periphery of the PDP 40: those power cable blocks havetwo outer stations with both inputs and CRDM outputs and a middlestation that has only CRDM outputs.

With continuing reference to FIG. 6 and with further reference to FIGS.9 and 10, a signal cable module 70 is shown having a similarconfiguration to the power module 60 of FIGS. 7 and 8. The signal cablemodule 70 of FIGS. 9 and 10 again includes an end input block 77 and twoconnection blocks 79, one in the middle and the other at the oppositeend from the input block. As with the power cable modules, variousconfigurations are possible for the signal cable modules: for example,in the distribution plate of FIG. 5 the upper rightmost signal cablemodule 70 has only an input block and a single connection block.

With particular reference to FIG. 11, in the embodiment shown, hydrauliclines 78 run in the receptacles/grooves 42 of the PDP 40 that receivethe power cable modules 60, and are overlaid by the installed powercable modules 60. (Note that FIG. 11 is diagrammatic in that it showsthe hydraulic lines 78 which are actually mostly or completely occludedby the overlaid installed power cable modules 60). The power cablemodules 60 also have openings 65 (labeled in FIGS. 7 and 8) throughwhich hydraulic connections that connect with the hydraulic lines 78 areaccessed.

This arrangement of power and signal cable modules 60, 70 allows thedisclosed distribution plate to be more modular during construction andservicing. The power cable modules 60 (shown in FIGS. 7 and 8) allow theremoval of a failed MI cable or electrical connector (along with thoseneighboring MI cables and connectors that are part of the same powercable module) while removing only a few CRDMs in the neighborhood of thefailed power MI cable. Similar considerations apply to a failed signalMI cable or connector. When the PDP 40 assembly is broken down, all ofthe MI cables and electrical connectors come out with the cable modules60, 70, leaving the hydraulic lines 78 and their connectors behind. Thisexposes the hydraulics to allow for service within the PDP. If only onehydraulic line or connector needs servicing, then only the power cablemodule overlying that hydraulic line needs to be removed. These featuresallow for modularity and serviceability of the distribution plate,simplifying manufacturing and servicing, reducing outage times.

The PDP 40 with its installed cable modules 60, 70 is the interface tothe CRDMs 20, and supports or houses all electrical cabling andhydraulics, and provides all connector receptacles. This allows a CRDM20 to be removed and replaced relatively routinely. The interface pointscould be at any location along the length of the CRDM 20, but placingthe interface point (the point at which the CRDM is broken from theupper internals) at the bottom of the CRDM allows the PDP to have arelatively flat face which simplifies installation and removal of theCRDMs. Optionally, a CRDM standoff connects the CRDM and the powerdistribution plate 40; alternatively, the CRDM can connect directly tothe plate.

Enclosing the electrical cabling and hydraulic lines in the PDP 40, asin the illustrative embodiment, provides protection from flow inducedvibrations (FIV). It also provides a direct load transfer of the weightof the CRDMs 20 to the mid hanger plate 50 (see FIG. 4). The mid hangerplate 50 also provides structural support for the PDP 40. In otherembodiments, the PDP is of sufficient thickness to structurally supportthe CRDMs directly. In other words, the PDP and the mid-hanger plate areintegrated together in these embodiments. In yet other embodiments, thePDP is not associated with the CRDM structural support at all, andprovides only power distribution functionality. This is the case, forexample, if the PDP is located below the mid-hanger plate, or if theCRDM units are supported from above (i.e. suspended from an upper hangerplate) rather than bottom-supported. As yet another variant, the PDP maybe integrated with or connected with an upper hanger plate located abovethe CRDMs (and the PDP may or may not bear the suspension load of theCRDMs in such embodiments).

The electrical connection of the CRDM 20 to the PDP 40 (with itsinstalled cable modules 60, 70) can be by various techniques. In someembodiments, conventional MI cable junctions and hydraulic connectionsare employed. In such embodiments, the servicing entails making/breakingMI cable junctions at the reactor, which can be labor-intensive andraises the potential for detrimental water ingress to the mineralinsulation of the MI cables. In an alternative approach, “quick connect”connections may be employed, in which the MI cables of the CRDMterminate in male plugs that connect with mating female receptacles ofthe cable modules 60, 70 (or vice versa), with the weight of the CRDM 20being sufficient (optionally along with suitable fasteners) to ensure anelectrically conductive connection between the male plugs and femalemating receptacles. Similarly, “quick connect” hydraulic connections maybe employed, in which the hydraulic lines of the CRDM terminate in malenozzles that connect with mating female receptacles of the hydrauliclines 78 (or vice versa), with the weight of the CRDM 20 beingsufficient (optionally along with suitable fasteners) to form a(possibly leaky) hydraulic connection. (The working fluid is assumed tobe purified primary coolant water, for example from a reactor coolantinventory and purification system, RCIPS). Such “plug-and-play”connection designs are further described in U.S. Ser. No. 13/405,405filed Feb. 27, 2012 entitled “Control Rod Drive Mechanism (CRDM)Mounting System For Pressurized Water Reactors”, first named inventorScott J. Shargots, which is incorporated herein by reference in itsentirety. When plug-and-play connections are employed, in-servicereplacement of a failed CRDM is further simplified. The CRDM is pulledby removing the hold-down bolts and then lifted from its position. Theplug-and-play connectors easily break between the CRDM and the powerdistribution plate. A new CRDM is then lowered into the vacatedposition. The connectors again function to connect the new CRDM to thepower source and hydraulic supply of the upper internals. Anotheradvantage to the CRDM plug and play method involves the manufacturingflexibility, since the male plugs and female receptacles can beinstalled at the factory where suitably dry conditions can be maintainedto avoid water ingress into the mineral insulation.

With returning reference to FIG. 6, an overhead view is shown of aportion of the PDP 40 with power and signal cable modules 60, 62installed. The power cable module 60 has electrical power connections 64and openings 65 (labeled in FIGS. 7 and 8) to accept hydraulicconnections 66. The signal cable module 70 has sensor connections 68 forrod position indication and rod bottom indication. Other sensors, suchas CRDM temperature or current, may also have connectors (not shown).The sensors may all use identical connectors and one connector may servemultiple sensors, although different types of connectors may also beused to prevent the CRDM from being installed in an incorrectorientation. Alternatively, the connection site of the CRDM may be keyedto prevent improper installation of the CRDM.

FIGS. 7 and 8 show alternative perspective views of one power cablemodule 60, with FIG. 7 tilted to show the top of the module and FIG. 8tilted to show the bottom of the module. FIG. 7 shows the top of themodule 60 and the electrical power connections 64. The electrical powerconnection provides power to the CRDM motor and may provide latchingpower if the latching mechanism is electrical. Openings 65 accept thehydraulic connectors 66 (see FIG. 5) when the module 60 is installed inthe receptacle 42 (see FIG. 3) of the PDP 40. The hydraulics provide thelatching power if a hydraulic latching mechanism is employed. FIG. 8shows the bottom of the power cable module 60 with installed power MIcabling 61.

FIGS. 9 and 10 show alternative perspective views of one signal cablemodule 70, with FIG. 9 tilted to show the top of the module and FIG. 10tilted to show the bottom of the module. The PI connectors (several ofwhich are labeled 74) connect to the position indicator cables of theCRDMs 20. The signal MI cables 71 are visible in FIG. 10, and connect tothe PI connectors 74.

With general reference to FIGS. 7-10, the undersides of the cablemodules 60, 70 are constructed so that when the cable modules 60, 70 areinstalled in the receptacles 42 of the PDP 40 (see FIG. 3), a cableconduit or raceway is defined between the module and the PDP. In theillustrative cable modules 60, 70, this is achieved by having peripheral(i.e. side) standoffs 80, 82 at the periphery of the modules that raisethe tops of the modules to define the cable conduit or raceway. Thehydraulic lines 78 shown in FIG. 11 are mounted to the PDP 40 inside thereceptacles 42 for the power cable modules 60, and the aforementionedconduit or raceway also houses the hydraulic lines 78. The hydrauliclines are attached to the PDP 40 in the illustrative embodiment, butalternatively may be attached to the modules (or omitted entirely if theCRDMs do not employ hydraulic power).

While the disclosed PDP with installable cable modules is described inconjunction with powering CRDM units, it is also suitable for poweringinternal electrically driven reactor coolant pump (RCP) units. Forexample, if internal RCP's are disposed on (or in) an annular pump platein the downcomer annulus, then the PDP could suitably be an annularplate mounted on the pump plate (a two-plate design) or, if thickenough, serving as the pump plate (a one-plate design).

The preferred embodiments have been illustrated and described.Obviously, modifications and alterations will occur to others uponreading and understanding the preceding detailed description. It isintended that the invention be construed as including all suchmodifications and alterations insofar as they come within the scope ofthe appended claims or the equivalents thereof.

I claim:
 1. An apparatus comprising: a nuclear reactor comprising apressure vessel containing primary coolant water and further containing:a nuclear reactor core comprising fissile material, a mounting platesecured entirely within the pressure vessel, a set of electric devicessupported by the mounting plate wherein the set of electric devices isone of (1) a set of control rod drive mechanism (CRDM) units and (2) aset of reactor coolant pumps (RCPs), a distribution plate mountedadjacent one of a top surface and a bottom surface of the mountingplate, the distribution plate being configured to be submerged in theprimary coolant, and a plurality of cable modules mounted in receptaclesof the distribution plate wherein each cable module includes mineralinsulated (MI) cables connected with one or more of the electricdevices, the cable module including its MI cables being removable as aunit from the receptacle of the distribution plate, wherein the set ofelectrical devices is mounted directly to one of the mounting plate andthe distribution plate.
 2. The apparatus of claim 1 wherein the set ofelectric devices is a set of CRDM units.
 3. The apparatus of claim 2wherein each CRDM unit includes a plurality of electrical powerconnectors mating with corresponding electrical power connectors of oneor more of the cable modules.
 4. The apparatus of claim 2 wherein eachCRDM unit includes a plurality of electrical power connectors matingwith corresponding electrical power connectors of exactly one of thecable modules.
 5. The apparatus of claim 2 wherein: the distributionplate has a plurality of openings through which connecting elements passthat connect the CRDM units with control rods comprising neutronabsorbing material, the CRDM units being configured to move the controlrods into and out of the nuclear reactor core via the connectingelements.
 6. The apparatus of claim 5 wherein: the distribution plate ismounted adjacent the bottom surface of the mounting plate below the setof CRDM units, and the mounting plate has a plurality of openingsaligned with the openings of the distribution plate through which theconnecting elements pass.
 7. The apparatus of claim 1 wherein: Thedistribution plate includes a set of hydraulic lines disposed on or inthe distribution plate and connected with the electric devices.
 8. Theapparatus of claim 7 wherein: each electric device of the set ofelectric devices includes a hydraulic connector mating with acorresponding hydraulic connector of the set of hydraulic lines.
 9. Theapparatus of claim 7 wherein the cable modules mounted in thereceptacles of the distribution plate overlay the set of hydrauliclines.
 10. The apparatus of claim 9 wherein the cable modules defineconduits or raceways through which the set of hydraulic lines run. 11.The apparatus of claim 1 wherein each cable module cooperates with thereceptacle of the distribution plate in which the cable module mounts todefine a conduit or raceway through which the MI cables of the cablemodule run.
 12. The apparatus of claim 11 wherein each cable moduleincludes standoffs at the periphery of the cable module to define theconduit or raceway through which the MI cables of the cable module run.13. The apparatus of claim 1 wherein the distribution plate is mountedon the top surface of the mounting plate below the set of electricdevices.
 14. The apparatus of claim 13 wherein the set of electricdevices is mounted directly on the distribution plate which transfersthe weight load of the electric devices to the mounting plate.
 15. Anapparatus comprising: a nuclear reactor comprising a pressure vesselcontaining primary coolant water and further containing: a nuclearreactor core comprising fissile material, a mounting plate securedentirely within the pressure vessel, a distribution plate mountedadjacent a top surface of the mounting plate, and a set of electricdevices mounted directly on the distribution plate, wherein thedistribution plate includes mineral insulated (MI) cables disposed in oron the distribution plate and connected with the set of electricdevices, wherein the set of electric devices is one of (1) a set ofcontrol rod drive mechanism (CRDM) units and (2) a set of reactorcoolant pumps (RCPs), and wherein the distribution plate is incapable ofsupporting the weight of the set of electric devices, the distributionplate transferring weight of the set of electric devices to the mountingplate which supports the combined weight of both the set of electricdevices and the distribution plate.
 16. The apparatus of claim 15wherein the distribution plate comprises: a plate having a plurality ofgrooves; and cable modules disposed in the grooves of the plate, eachcable module including a portion of the MI cables disposed on or in thedistribution plate, each cable module including its portion of the MIcables being removable from the plate as a unit.
 17. The apparatus ofclaim 15 wherein the set of electric devices is a set of control roddrive mechanism (CRDM) units.